The goal of this program is to develop an effective vaccine against human immunosuppressive virus (HIV-1) infection and the resultant Acquired Immunodeficiency Syndrome (AIDS). The strategy is twofold: (1) to utilize recombinant vaccinia viruses expressing HIV-1 or Simian Immunodeficiency Virus (SIV) antigens to induce immunity, and (2) to utilize the SIV model for evaluation of different recombinant vaccine prototypes as a indicator for corresponding recombinant HIV-1 vaccine performance. Evaluation of recombinant SIV and HIV-1 vaccines will include determination of: vaccine antigenicity in various laboratory animal species (including primates by determination of humoral and cell- mediated immune responses; protective immunity and meliorative properties of recombinant vaccines in primates before and after challenge with SIV: toxicity of vaccinia vectors in SIV-infected primates; safety evaluation in primates of final HIV-1 vaccine candidates. Research assigned to this specific Research Project as a part of the National Cooperative Vaccine Development Group for the Acquired Immunodeficiency Syndrome (NCVDG) will be performed at EG&G Mason Research Institute (EG&G MRI), the New England Regional Primate Research Center (NERPRC), and the University of Massachusetts Medical School (UMMS). This research will be coordinated by the Project Leader at EG&G MRI, Worcester, MA in collaboration with research and administrative support provided by the Principal Investigator at Applied bioTechnology, Cambridge, MA.